The invention relates generally to fuel delivery systems, and more particularly to a method and system for controlling delivery of gaseous fuel to an internal combustion engine.
Alternative gaseous fuels, such as compressed natural gas ("CNG"), for use in internal combustion engines are generally known. A common characteristic of these gaseous fuels is that in comparison to gasoline a much greater volume is required to store an amount of energy necessary to obtain an equivalent range of travel. In order to obtain a range of travel comparable to gasoline without exceeding the space available for fuel storage, natural gas is typically compressed to pressures as high as 3600 psig or even higher.
Typical solenoid operated fuel injectors cannot be opened once the pressure exerted on the valve needle by the fuel exceeds the maximum electromotive force which can be generated to pull the valve needle away from the valve seat, typically 150 psig. Accordingly, most CNG fuel delivery systems provide a pressure regulator to reduce the CNG stored pressure to an operating pressure of around 90-115 psig.
When the pressure exerted by the fuel on the fuel injector needle exceeds the maximum electromotive force developed at the valve needle, the excess pressure should be relieved. Numerous federal regulations, however, prohibit the release of CNG into the atmosphere above certain volumes. Accordingly, a need exists for a method and system of controlling delivery of gaseous fuel to an internal combustion engine which provides a means for relieving pressure at the fuel injectors without introducing the gaseous fuel into the atmosphere.